JDK动态代理手写实现

MyProxy.java:模拟Proxy

package com.proxy;

import java.io.File;

import java.io.FileWriter;

import java.io.IOException;

import java.lang.reflect.Constructor;

import java.lang.reflect.InvocationTargetException;

import java.lang.reflect.Method;

import javax.tools.JavaCompiler;

import javax.tools.JavaCompiler.CompilationTask;

import javax.tools.StandardJavaFileManager;

import javax.tools.ToolProvider;

/**

• 模拟实现jdk动态代理 (基于接口实现)
• @author Administrator
• */
• public class MyProxy {
• static String rt = "\r\t";
• static String packageDir="com.proxy";

/**

• 此方法为产生代理对象的方法
• @param loader
• 类加载器
• @param interfaces
• 代理接口类(原jdk里面是数组 因为一个类可以实现多个接口)
• @param h
• 代理对象
• @return
• */
• public static Object newProxyInstance(ClassLoader loader, Class interfaces,
• MyInvocationHandler h) {
• String javaDir = "src/"+packageDir.replace(".", "/");
• String javaName = "$Proxy0";
• String fileName = javaDir + "/" + javaName + ".java";
• // 1产生动态代理类源文件 get$proxy0.java
• String javaFileStr = get$Proxy0(interfaces);
• // 2生成源文件
• createJavaFile(javaFileStr, fileName);
• // 3编译源文件
• compilerJava(fileName);

// 4加载类 生成Class对象

Class cls=findClass(javaDir,javaName);

// 5构建代理对象

Object obj=newInstance(cls,h);

//6 删除文件

deleteFile(fileName);

return obj;

}

private static void deleteFile(String fileName) {

// TODO Auto-generated method stub

File file=new File(fileName);

file.delete();

}

private static Object newInstance(Class cls, MyInvocationHandler h) {

// TODO Auto-generated method stub

Constructor cons;

Object obj=null;

try {

cons = cls.getConstructor(MyInvocationHandler.class);

obj=cons.newInstance(h);

} catch (NoSuchMethodException e) {

// TODO Auto-generated catch block

e.printStackTrace();

} catch (SecurityException e) {

// TODO Auto-generated catch block

e.printStackTrace();

} catch (InstantiationException e) {

// TODO Auto-generated catch block

e.printStackTrace();

} catch (IllegalAccessException e) {

// TODO Auto-generated catch block

e.printStackTrace();

} catch (IllegalArgumentException e) {

// TODO Auto-generated catch block

e.printStackTrace();

} catch (InvocationTargetException e) {

// TODO Auto-generated catch block

e.printStackTrace();

}

return obj;

}

private static Class findClass(String javaDir, String javaName) {

// TODO Auto-generated method stub

MyClassLoader myloader = new MyClassLoader(javaDir);

Class cls = null;

try {

cls = myloader.findClass(javaName);

} catch (ClassNotFoundException e) {

// TODO Auto-generated catch block

e.printStackTrace();

}

return cls;

}

// 通过代码编译java

private static void compilerJava(String fileName) {

JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();// 获取编译器

StandardJavaFileManager fileMgr = compiler.getStandardFileManager(null,

null, null);

Iterable units = fileMgr.getJavaFileObjects(fileName);

CompilationTask task = compiler.getTask(null, fileMgr, null, null,

null, units);

task.call();

try {

fileMgr.close();

} catch (IOException e) {

// TODO Auto-generated catch block

e.printStackTrace();

}

}

// 生成java文件

private static void createJavaFile(String javaFileStr, String fileName) {

File file = new File(fileName);// File类

FileWriter fw = null;

try {

fw = new FileWriter(file);

fw.write(javaFileStr);

fw.flush();

} catch (IOException e) {

e.printStackTrace();

} finally {

if (fw != null) {

try {

fw.close();

} catch (IOException e) {

}

}

}

}

/**

• 拼接代理类字符串
• @return
• */
• private static String get$Proxy0(Class interfaces) {
• StringBuffer javaFile = new StringBuffer("package com.proxy;" + rt);// 定义包
• javaFile.append("import java.lang.reflect.Method;" + rt);// 导入包
• javaFile.append("public class $Proxy0 implements "
• interfaces.getName() + "{" + rt);// 定义类实现接口
• javaFile.append("MyInvocationHandler h;" + rt);// 定义代理对象
• javaFile.append("public $Proxy0(MyInvocationHandler h){" + rt);
• javaFile.append("this.h=h;" + rt);
• javaFile.append("}" + rt);
• javaFile.append(getMethodStr(interfaces.getMethods(), interfaces) + rt);// 拼接方法
• javaFile.append("}" + rt);
• return javaFile.toString();
• }

/**

• 方法的拼接
• @return
• */
• private static String getMethodStr(Method[] methods, Class infs) {
• // TODO Auto-generated method stub
• StringBuffer methodStr = new StringBuffer();// 方法字符串
• for (Method method : methods) {// 遍历方法对象
• methodStr.append("public void " + method.getName() + "() throws Throwable {" + rt);
• methodStr.append("Method md=" + infs.getName()
• ".class.getMethod(\"" + method.getName()
• "\",new Class[]{});" + rt);
• methodStr.append("this.h.invoke(this,md,null);" + rt);
• methodStr.append("}" + rt);
• }
• return methodStr.toString();
• }
• }
• MyInvocationHandler.java 模拟InvocationHandler
• package com.proxy;

import java.lang.reflect.Method;

/**

• 定义代理拦截器
• @author Administrator
• */
• public interface MyInvocationHandler {
• /**
• 代理接口实现方法
• @param proxy 代理对象
• @param method 代理方法
• @param args 参数
• @return 返回源目标方法结果
• @throws Throwable 异常声明
• */
• public Object invoke(Object proxy, Method method, Object[] args) throws Throwable;
• }
• MyClassLoader.java 实现自定义类加载器
• package com.proxy;

import java.io.ByteArrayOutputStream;

import java.io.File;

import java.io.FileInputStream;

import java.io.FileNotFoundException;

import java.io.IOException;

/**

• 自定义类加载器
• @author Administrator
• */
• public class MyClassLoader extends ClassLoader {
• private File dir;
• public MyClassLoader(String filePath){
• dir=new File(filePath);
• }
• @Override
• /**
• 找类
• */
• protected Class<?> findClass(String name) throws ClassNotFoundException {
• // TODO Auto-generated method stub
• if(dir!=null){
• File classFile=new File(dir,name+".class");
• if(classFile.exists()){
• FileInputStream fis=null;
• try {
• fis=new FileInputStream(classFile);
• //创建字节数组流对象
• ByteArrayOutputStream bais=new ByteArrayOutputStream();
• //创建字节数组
• byte[] buffer=new byte[1024];
• int len=0;
• while((len=fis.read(buffer))>0){//循环读取
• bais.write(buffer, 0, len);
• }
• //bais.size() 字节流大小
• Class cls=defineClass(MyProxy.packageDir+"."+name, bais.toByteArray(), 0, bais.size());
• return cls;
• } catch (FileNotFoundException e) {
• // TODO Auto-generated catch block
• e.printStackTrace();
• } catch (IOException e) {
• // TODO Auto-generated catch block
• e.printStackTrace();
• }finally{
• if(fis!=null)try {fis.close();} catch (IOException e) {e.printStackTrace();}
• }
• }
• }
• return super.findClass(name);
• }
• }
• Person.java代理接口类
• package com.proxy;

/**

• jdk动态代理实现 基于接口实现
• 人类接口
• @author Administrator
• */
• public interface Person {

/**

• 吃的方法
• */
• public void eat() throws Throwable;
• }
• PersonInvocationHandler.java 代理目标对象类
• package com.proxy;

import java.lang.reflect.Method;

/**

• jdk动态代理对象
• @author Administrator
• */
• public class PersonInvocationHandler implements MyInvocationHandler {
• //代理目标对象
• private Object target;
• //构造方法 传入代理目标对象
• public PersonInvocationHandler(Object target){
• this.target=target;
• }
• @Override
• //proxy 生成的代理对象
• public Object invoke(Object proxy, Method method, Object[] args)
• throws Throwable {
• before();
• method.invoke(target, args);
• after();
• return null;
• }
• public void before(){
• System.out.println("吃饭前洗手");
• }
• public void after(){
• System.out.println("吃饭后漱口");
• }
• }
• ZhanSan.java 目标对象类
• package com.proxy;

public class ZhanSan implements Person {

@Override

public void eat() {

System.out.println("吃饭的方法");

}

}

Test.java测试类

package com.proxy;

public class Test {

/**

• @param args
• @throws Throwable
• */
• public static void main(String[] args) throws Throwable {
• // TODO Auto-generated method stub
• Person person=new ZhanSan();
• MyInvocationHandler handler=new PersonInvocationHandler(person);
• person=(Person)MyProxy.newProxyInstance(Test.class.getClassLoader(), Person.class, handler);
• person.eat();
• }

}